Embodiments of the present invention relate to solid-state batteries and their fabrication methods.
Solid-state batteries are used in applications that require a battery with a high energy density such as, for example, portable electronics, medical devices and space systems. A typical solid-state battery comprises a support to hold one or more battery cells, each cell having a set of battery component layers that include an electrolyte sandwiched between electrode layers, such as an anode, cathode, and anode and cathode current collectors or contact pads. The battery component layers cooperate to store electrical charge and generate a voltage. Solid-state batteries include larger scale structures used for computer and car batteries, and thin film batteries in which the battery component layers are thin films which have thicknesses of less than about 100 microns. Solid-state batteries can include one or more identical battery cells which are stacked together and connected in series or in parallel to provide more power or energy.
Solid-state and thin film batteries possesses many advantages over other battery systems, such as long battery cycle life, low battery capacity fade properties, a large operational temperature range, safety, and still others. However, solid-state and thin film batteries are difficult to fabricate, and operate in, high current applications which require high current density from the battery. A typical high current application for a solid-state, thin film battery is one which requires a current density of at least about 3 mA per cm2 of the active area of the solid-state or thin film battery. Solid-state, thin film batteries have limited high current applications because of the relatively low diffusion rates of the charge-carrying species which store or release electrical energy in a charged battery. The low diffusion rates occur because the charge carrying species need to diffuse through the entire thickness of the cathode to conduct current. Thus, many solid-state and thin film batteries generate current densities which are not sufficiently high for high current applications. For example, a lithium battery is a solid-state or thin film battery in which a lithium-containing material comprising lithium-containing species, such as lithium ions, is sandwiched between at least a pair of electrode layers. The lithium ions serve as the charge-carrying species of the battery cell. The lithium ion diffusion rate is generally lowest in the cathode of the battery cell because the lithium ions need to diffuse through a metal lattice, especially when the cathode is made thicker to provide battery cells having higher specific energies. These diffusion rates can limit the high output current density of the battery cell.
For these and other reasons, further developments and improvements in the structure and methods of fabricating solid-state and thin film batteries which can provide high output current density are continuously being sought.